BACKGROUND: Rapid and effective pain relief in acute traumatic limb injuries (ATLI) is one of the most important roles of emergency physicians. In these situations, opioid addiction is an important concern because of the dependency on opioids. The study aims to compare the effectiveness of intravenous (IV) fentanyl versus morphine in reducing pain in patients with opioid addiction who suffered from ATLI. METHODS: In this double-blind randomized clinical trial, 307 patients with ATLI, who presented to the emergency department (ED) from February 2016 to April 2016, were randomly divided into two groups. One group (152 patients) received 0.1 mg/kg IV morphine. The other group (155 patients) received 1 mcg/kg IV fentanyl. Patients' demographic data, pain score at specific intervals, vital signs, side effects, satisfaction and the need for rescue analgesia were recorded. RESULTS: Eight patients in the morphine group and five patients in the fentanyl group were excluded. Pain score in the fentanyl group had a significant decrease at 5-minute follow-up (P value=0.00). However, at 10, 30, and 60-minute follow-ups no significant differences were observed between the two groups in terms of pain score reduction. The rescue analgesia was required in 12 (7.7%) patients in the fentanyl group and in 48 (31.6%) patients in the morphine group (P value=0.00). No significant difference was observed regarding side effects, vital signs and patients' satisfaction between the two groups. CONCLUSION Fentanyl might be an effective and safe drug in opioid addicts suffering from ATLI.